Do I really need an Anti-virus?

Virtually, no one who uses Windows-based computers is immune from viruses. Every time your computer handles a new file, chances are that it could be infected. In particular, that is the case when you open attachments in your emails, when you download a program from the Internet or when you copy a file from one computer to another. Unless your computer is completely isolated from the outside world, which would make it pretty useless, the risk of infections are quite high.

There are 60,000 to 70,000 active viruses and worms, with 10,000 new ones appearing every year. Nearly all are designed to infect Windows PCs. That means that Mac users don't need anti-virus protections because their machines can not run any program written for Windows, including viruses.

At the moment, it's safe to say that a Mac user would need an anti-virus only when a Windows emulator like Virtual PC is used. That would be required to protect the Windows environment only, because Windows-viruses can not run and damage OS X.